If the cracks are small (>1mm but <10mm) and there is no problem with the structure, use a flexible crack filling compound, Nerolac Perma Crack Filler, for filling the cracks. Unlike cement that permits seepage, Nerolac Perma Crack Filler is waterproof and is ideal for small cracks.

Post that a proper waterproofing to be done with an elastomeric product which has crack bridging properties to tackle the issue of hairline cracks like Nerolac Perma NoDamp.